UNIVERSITY   OF    CALIFORNIA        AGRICULTURAL  EXPERIMENT  STATION 
COLLEGE   OF  AGRICULTURE  BENJ    ,DE  WHEELER-  >««">»» 

THOMAS    FORSYTH     HUNT,    DEAN   AND   DIRECTOR 

BERKELEY  H.    E.   VAN    NORMAN,    vice-director    and    Dean 

University    Farm    School 

CIRCULAR  No.  137 

(September,    1915) 

WOOD  DECAY  IN  ORCHARD  TREES 

By  WILLIAM   TITUS   HORNE 


Much  study  has  been  given  to  the  rots  of  timber,  both  before  and 
after  it  is  cut,  but  the  decays  of  orchard  trees  apparently  have  never 
been  thoroughly  investigated. 

During  the  winter  of  1913-14,  Mr.  C.  J.  Rodgers,  one  of  our 
students,  discovered  that  the  so-called  sappy  bark  disease  of  apples  is 
due  to  a  wood  rot.  This  disease  is  one  of  the  most  serious  affecting 
the  life  of  apple  trees  in  California.  Slow-working,  and  only  attack- 
ing here  and  there  a  tree  with  large  wounds,  it  nevertheless  causes 
tree  after  tree  to  weaken  generally  and  break  down  and  die. 

Mr.  W.  W.  Thomas,  another  of  our  students,  has  investigated  wood 
rots  in  stone  fruits  with  the  surprising  result  of  finding  that  some 
orchards  have  scarcely  a  sound  tree,  and  that  hardly  any  bearing 
orchard  is  free  from  wood  decays.  He  found  that  the  trouble  is 
serious  all  over  the  main  deciduous  fruit  regions,  and  that  about  one- 
half  the  bearing  trees  are  already  seriously  infected,  while  almost  all 
of  the  trees  still  sound  are  in  a  condition  easily  to  become  infected. 

No  practical  remedy  is  known  for  decayed  trees  and  almost  nothing 
is  being  done  to  prevent  infection.  During  the  next  decade  the  loss 
from  deterioration  and  breaking  down  of  trees  now  attacked  must 
be  very  heavy.  From  this  it  appears  that  the  subject  should  be  care- 
fully investigated  and  the  facts  made  available  to  all  the  growers. 

Symptoms  of  Wood  Decay. — Wood  decay  is  an  insidious  disease 
developing  within  the  tree.  It  is  not  visible  from  the  exterior  until 
in  some  way  the  surface  of  the  tree  is  broken,  exposing  the  decayed 
or  hollow  interior.  The  rot  starts  in  some  area  of  dead  bark  or  exposed 
wood,  but  drying  protects  the  visible  outer  surface,  so  that  it  remains 
intact  long  after  the  rot  is  established  and  far  advanced.  Often  there 
is  sunburn  and  gumming  of  the  decaying  limbs,  but  nothing  abnormal 
may  be  noticed  until  a  large  branch  gives  way  under  some  unusual 
strain  and  the  center  is  seen  to  be  decayed.  The  tree  may  continue 
to  bear  well  for  some  time,  but  finally  breaks  down. 


There  are  several  types  of  decay  but  the  commonest  is  a  light- 
colored  rot,  in  which  there  is  at  first  a  slight  darkening  of  the  wood, 
after  which  it  grows  lighter  in  color  and  softer  in  texture  until 
little  is  left  except  a  very  light  powdery  material.  From  the  point 
of  starting  the  rot  spreads  faster  through  the  center  of  the  trunk 
than  laterally.  Often  decay  works  outward  so  slowly  that  the  tree 
becomes  hollow  and  remains  standing  for  many  years.  But  in  the 
case  of  sappy  bark  of  the  apple  Mr.  Rodgers  has  observed  that  the 
outward  spread  of  decay  in  the  wood  causes  the  death  of  the  cambium 
and  bark,  giving  rise  to  extensive  dead  areas  or  cankers,  which  enlarge 
each  winter  until  the  limb  is  killed  or  breaks  off.  On  the  dead  limbs 
or  parts,  fungus  bodies — brackets,  conches,  hoof  fungi,  punks,  or 
toadstools — often  appear.  These  fungus  bodies  are  generally  the 
spore-bearing  part  of  the  fungus  which  caused  the  rot  of  the  wood. 
In  some  cases  the  fungus  fruits  are  small  or  inconspicuous,  and 
often  well-advanced  decay  is  found  without  any  sort  of  fungus  fruit. 
After  some  practice  a  trained  mycologist  can  tell  with  considerable 
accuracy  what  fungus  caused  the  rot  by  the  color,  texture,  and  other 
characteristics  of  the  decaying  wood.  The  final  result  is  that  one 
branch  after  another  dies  or  is  broken  off  while  still  vigorous.  The 
whole  tree  may  break  off,  but  more  generally  one  limb  goes  at  a 
time  until  nothing  but  a  worthless  stump  is  left. 

Cause  of  Wood  Decay. — Wood  decay  is  not  caused  by  exposure  to 
air  and  moisture.  Neither  is  it  directly  caused  by  lack  of  thrift  or 
old  age  of  the  trees.  Untreated  shingles  on  the  side  of  a  house 
weather  gradually  and  would  doubtless  disappear  in  time,  but  there 
is  no  reason  why  the  wood  of  a  tree  should  deteriorate.  Wood  decay 
is  due  to  the  action  of  certain  fungi  which  have  the  power  of  pene- 
trating into  the  wood  and  digesting  it.  Not  all  fungi  have  this  power, 
and  not  more  than  about  a  dozen  species  have  been  found  causing 
serious  harm  in  orchard  trees  in  California.  Of  these  the  oyster- 
shell  fungus  (species  of  the  genus  Polystictus  or  Coriolus)  does  more 
harm  than  all  the  others  combined.  The  fruits  of  this  fungus  some- 
what resemble  a  small  oyster  shell,  gray  or  brown  with  dark  bands 
on  the  upper  surface,  and  light-colored  with  vertical  pores  or  minute 
tubes  on  the  lower.  There  are  several  closely  related  species  which, 
so  far  as  observed,  appear  to  act  in  very  much  the  same  way.  Micro- 
scopic spores  are  formed  in  great  numbers  on  the  sides  of  the  tubes 
and  fall  out,  to  be  carried  away  by  the  wind  or  by  other  agents. 
The  spores,  if  kept  from  direct  sunlight  or  extreme  drying,  may  live 
for  weeks  or  even  months,  and  grow  when  sufficient  moisture  is 
furnished.     There  is  every  reason  to  believe  that  cracks  in  exposed 


pruning  wounds  are  very  favorable  places  for  the  spores  to  grow,  if 
once  they  find  their  way  into  these  places. 

The  fruiting  bodies  (sporophores  or  brackets)  have  remarkable 
resistance  to  drying.  Taken  from  a  woodpile  in  the  San  Joaquin 
Valley  at  the  end  of  summer,  and  moistened,  they  have  produced 
vigorous  spores  in  a  few  hours.  Specimens  eaten  by  beetles  until 
only  shreds  remained  still  produced  spores  when  moistened.  The 
fungus  mycelium  living  in  dead  sticks  will  remain  alive  for  several 
years  if  the  wood  is  kept  in  a  dry  place.  During  one  winter  a  single 
fruiting  body  may  produce  millions  of  spores,  each  one  of  which  is 
capable  of  infecting  a  wound  if  it  comes  in  contact  with  the  wood 
and  is  kept  sufficiently  moist.  Nevertheless  part  of  the  trees  in  an 
orchard  usually  remain  free  from  rot  for  a  time,  although  having 
large  cracked  wounds.  This  suggests  that  the  spores  do  not  happen 
to  be  carried  to  all  wounds,  or  fail  to  grow  successfully  in  them. 

There  are  several  fungi  which  are  found  occasionally  associated 
with  rot,  and  they  doubtless  cause  it  in  most  cases.  Further  study 
may  considerably  increase  the  list,  but  the  principles  of  distribution 
and  growth  will  apply  rather  closely  to  all,  excepting  the  oak  root 
fungus  and  a  few  other  true  parasites. 

Nature  of  the  Process. — Wood  decay  consists  of  a  series  of  chemical 
changes  brought  about  by  the  action  of  the  fungus  threads  or  mycelium, 
and  is  a  process  of  digestion  and  absorption.  Wood  substance  is  com- 
posed of  carbon,  hydrogen,  and  oxygen,  and,  chemically,  it  rather 
closely  resembles  starch  or  sugar.  Besides  the  wood  substance  proper 
there  are  some  other  materials  in  wood,  such  as  the  mineral  consti- 
tuents or  ash.  The  digestion  of  wood  consists  in  its  change  into  some 
substance  like  sugar,  which  is  then  used  by  the  fungus  for  food,  the 
final  result  being  that  carbon  and  oxygen  are  combined  to  make  carbon 
dioxid  (carbonic  acid  gas)  which  escapes  to  the  air,  and  the  hydrogen 
is  combined  with  oxygen  to  form  water,  which  may  easily  be  evaporated 
and  disappear.  Where  the  decay  of  wood  is  complete  little  is  left 
except  ash. 

Manner  of  Infection. — The  precise  manner  in  which  infection  act- 
ually occurs  is  not  easy  to  observe,  since  decay  must  develop  to  a 
certain  stage  before  being  recognizable.  Small  wounds  and  wounds 
not  cracked  seldom  decay.  Deeply  cracked  wounds,  especially  when 
large,  generally  are  found  with  decay  below  them,  and  all  evidence 
points  to  the  cracks  in  exposed  wood  as  the  places  where  infection 
occurs.  Evidently  spores  of  wood-destroying  fungi  fall  into  the 
cracks.  With  wet  weather  the  spores  are  kept  moist  until  they  grow 
and  form  mycelium,   which  penetrates   into  the  wood   and  becomes 


established.  The  stubs  left  in  grafting-over  large  limbs  are  about  the 
surest  places  of  all  for  infection.  A  rather  generous  area  of  wood  is 
exposed  and  this  almost  always  cracks  deeply.  The  cracks  are  usually 
so  placed  that  wind-borne  spores  could  easily  fall  into  them,  or,  if 
deposited  from  the  feet  of  birds  or  insects  on  the  top  of  the  stub, 
they  would  be  beaten  into  the  cracks  by  rain.  Sometimes  a  stub  heals 
over  after  decay  has  become  established  in  the  wood,  and  internal 
infection  is  only  shown  by  the  breaking  of  the  tree  or  by  the  dying  of 
some  part  of  it  and  the  emergence  of  fruits  of  the  fungus.  The  danger 
of  infection  in  any  wound  is  not  passed  until  the  bark  has  completely 
healed  over. 

The  manner  in  which  fungus  spores  are  carried  to  the  tree  wounds 
has  not  been  determined;  but  wind,  the  feet  of  insects  and  birds,  and 
various  other  agents,  may  play  a  part.  Mr.  Thomas  has  observed  that 
there  are  often  groups  of  trees  affected  with  the  same  kind  of  rot 
fungus  indicating  that  it  has  spread  from  an  original  source,  or  from 
tree  to  tree  locally. 

The  oak  root  fungus  causes  rot  of  the  wood  of  roots  and  the  lower 
part  of  the  trunk,  after  having  killed  the  living  root.  It  is  confined 
rather  closely  to  the  roots  and  bases  of  trees.  It  freely  attacks  and 
kills  living  bark,  differing  in  this  respect  from  the  ordinary  wood  rot 
fungi,  which  are  powerless  to  penetrate  through  sound,  living  bark 
into  the  wood  below. 

Source  of  Infection. — The  fungi  which  cause  wood  rot  in  the 
orchard  can  be  found  abundantly  in  the  native  growth,  especially  along 
wooded  streams.  Old  orchards  also  become  sources  of  infection.  The 
destruction  of  sporophores  in  a  well-isolated  orchard  would  reduce  the 
number  of  spores  present,  yet  birds  or  insects  might  easily  carry  spores 
for  several  miles. 

Susceptibility  of  Different  Fruit  Trees. — Observations  suggest  the 
following  order  of  susceptibility  of  orchard  trees  to  decay:  Peach, 
cherry,  apple,  plum  (including  prunes),  apricot,  walnut,  pear,  olive, 
and  citrus  trees.  Olive  and  citrus  trees  will  probably  become  hollow 
without  showing  the  more  violent  effects  of  rot,  such  as  sappy  bark 
of  apple,  but  even  they  must  be  to  a  certain  extent  crippled. 

Prevalence  of  Wood  Decay  in  Orchards. — It  is  well  recognized 
that  some  decaying  trees  occur  in  all  sections  and  in  nearly  all  orchards, 
especially  of  stone  fruits  and  apples.  The  actual  percentage  of  decayed 
trees  can  evidently  be  determined  only  by  careful  examination  of 
large  numbers  of  representative  orchards,  in  which  either  every  tree 
should  be  examined,  or  a  certain  number  of  trees  taken  in  a  way  to 
represent  the  whole.     A  number  of  examinations  of  both  kinds  have 


been  made  by  Mr.  W.  W.  Thomas  for  stone  fruits.  In  the  districts 
examined  in  central  California  it  appears  that  nearly  fifty  per  cent 
of  all  bearing  stone  fruit  trees  are  positively  infected  with  wood 
decay.  Of  the  remainder  not  more  than  about  two  per  cent  are  free 
from  large  cracked  wounds  which  may  already  be  infected  or  are  in 
great  danger  of  infection.  Orchards  which  are  not  very  old  can  be 
found  in  which  every  tree  has  decay.  Grafted-over  trees  usually 
show  a  very  high  proportion  of  decay,  frequently  approaching  a 
hundred  per  cent. 

It  might  be  supposed  that,  since  moisture  favors  the  growth  of 
fungi  and  fungus  spores,  decay  would  be  more  prevalent  in  the  moist 
coast  sections  than  in  the  drier  interior.  From  studies  made  to  date, 
the  reverse  appears  to  be  true.  Fruiting  bodies  and  spores  are  formed 
during  the  rainy  season  when,  normally  there  is  adequate  moisture  in 
all  sections.  Dry  air  in  summer  does  not  kill  the  sporophores  of  the 
worst  of  these  fungi,  but  only  suspends  the  production  of  spores. 
The  more  intense  the  heat  and  drying,  the  more  sunburned  and  dead 
limbs  will  occur,  and  the  more  deeply  the  exposed  wood  will  crack. 
Cracks  in  exposed  wood  appear  to  be  the  main  starting  points  of  rot. 
Accordingly  our  observation  that  the  more  trying  the  situation,  the 
more  prevalent  wood  rot  becomes,  appears  to  be  logical. 

No  accurate  estimates  can  be  made  of  the  annual  loss  to  California 
orchards  through  decay  of  trees,  since  the  comparative  production 
of  decaying  and  sound  trees  for  the  different  varieties  of  fruit  has 
never  been  carefully  studied.  Yet  if  we  consider  the  shortening  of 
the  life  of  the  tree,  together  with  its  original  cost,  the  expense  of 
planting  and  of  care  until  the  age  of  profitable  production,  and  the 
decrease  in  bearing  which  we  believe  occurs  when  the  tree  becomes 
decayed,  it  is  safe  to  say  that  wood  rot  in  stone  fruits  and  apples 
has  reduced  the  production  and  increased  the  expense  by  a  very  large 
percentage.  Professor  Wickson  states  that  the  peach  orchards  in 
central  and  northern  California  are  not  old  enough  to  mark  the  normal 
life  of  a  peach  tree,  and  the  best  authorities  seem  to  agree  that  fifty  or 
sixty  years  will  not  find  the  peach  tree  aged  except  by  the  entrance 
of  decay  into  the  wood.  Yet  the  usual  length  of  life  of  a  peach 
orchard  in  California  is  not  half  this  period. 

Treatment  of  Infected  Trees. — A  tree  with  well  established  decay 
presents  a  difficult  problem.  Tree  surgery  methods  may  be  employed, 
but,  where  decay  has  spread  far  through  the  center  of  a  tree,  the 
possibility  of  complete  elimination  is  very  doubtful.  The  expense 
of  endeavoring  to  remove  all  decayed  wood  will  usually  make  the 
operation  impractical.     The  use  of  a  cement  filling  in  orchard  trees 


6 

will  rarely  be  advisable.  Whatever  will  keep  the  decaying  wood  as 
dry  as  possible  is  probably  the  most  promising  procedure. 

Some  old  wounds  appear  to  have  mild  forms  of  decay.  It  would 
seem  reasonable  to  treat  such  cases  in  the  same  way  as  sound  wood,  to 
prevent  the  entrance  of  fungi  causing  the  more  rapid  rots.  Where 
soft,  active  rot  is  established,  sealing  up  the  wound  must  tend  to 
hasten  its  development  by  preventing  drying. 

Preventive  Measures. — The  greatest  importance  attaches  to  the 
proper  training  of  the  young  tree.  If  too  many  branches  are  left  in 
the  framework,  some  of  these  crowd  and  must  be  removed  later.  Often 
the  branch  to  be  removed  is  in  the  center  of  the  head,  and  a  clean, 
well-drained  cut  is  impossible.  The  picture  of  the  tree  when  it  is 
fully  grown  should  be  in  the  mind  of  the  man  shaping  the  young 
tree.  The  branches  which  form  the  framework  should  emerge  from 
the  main  stem  at  such  distances  that  they  will  not  crowd  in  the  mature 
tree,  since  they  do  not  separate  farther  in  the  subsequent  growth.  It 
is  difficult  to  grow  a  tree  with  sufficiently  spaced  framework  branches, 
from  a  conventional  nursery  tree,  treated  in  the  usual  way.  It  is 
not  possible  here  to  give  specific  directions  for  forming  the  framework 
of  trees,  nor  is  it  probable  that  one  system  of  pruning  or  another  will 
be  absolutely  essential;  however,  such  foresight  should  be  exercised 
in  any  system  that  the  subsequent  removal  of  large  limbs  will  not 
become  necessary  and  that  the  splitting  and  breaking  will  be  reduced 
to  a  minimum.  Summer  pinching  and  training  should  make  it  pos- 
sible to  reduce  greatly  the  severity  of  the  winter  pruning. 

Where  limbs  must  be  removed,  close  cutting  is  exceedingly  im- 
portant. Stubs  even  one-fourth  inch  longer  than  necessary  may 
delay  the  time  of  healing  for  several  years  and  accordingly  increase 
the  time  of  exposure  to  infection.  Long  stubs  dry  and  crack  more 
than  short  ones,  and  the  cracks  and  exposed  dead  bark  are  the  most 
favorable  places  for  infection. 

All  attempts  to  prevent  rot  by  treatment  of  the  cuts  have  been 
abandoned  in  many  good  orchards,  decay  being  found  quite  as  active 
in  painted  cuts  as  in  unpainted  ones.  We  have  observed  that  ordinary 
painting  does  not  prevent  the  formation  of  large  cracks;  and  these 
cracks  are  left  untreated.  //'  decay  is  to  be  prevented,  infection  of 
wounds  must  be  prevented,  and  the  following  method  is  recom- 
mended:* 

*  These  recommendations  are  not  made  on  the  basis  of  experiments  by  the 
writer,  but  on  that  of  the  safest  and   most   reliable   methods  in  tree   surgery. 


1.  All  cuts  should  be  made  close  to  the  trunk. 

2.  Where  limbs  three-fourths  of  an  inch  or  more  in  diameter  must 
be  removed,  the  cut  surface  should  be  immediately  wet  with  a  disin- 
fectant solution  (see  below). 

3.  As  soon  as  the  surface  is  dry  enough  to  hold  paint  well,  a 
sealing  paint  should  be  applied,  making  a  heavy  coat  over  the  sur- 
face (see  below). 

4.  In  September  of  each  year  all  trees  should  be  gone  over,  dead 
branches  should  be  removed,  all  dead  bark  from  sunburned  and  other 
injured  areas  should  be  carefully  trimmed  and  scraped  away,  and 
wounds  previously  treated  should  be  inspected.  Treat  all  exposed 
wood,  whether  a  new  cut  or  a  crack  in  a  painted  surface,  with  disin- 
fectant, and,  when  dry,  cover  with  sealing  paint.  A  good  sealing 
paint,  applied  in  September,  should  last  until  the  following  summer, 
and,  since  spores  must  be  in  contact  with  wood  in  moist  weather 
to  cause  infection,  one  treatment  per  year  should  protect  trees  in 
California. 

For  a  disinfectant,  corrosive  sublimate,  one  part  to  one  thousand 
parts  of  water,  is  recommended. 

For  a  sealing  paint,  asphaltum,  grade  D,  applied  hot,  is  recom- 
mended. Asphaltum,  thinned  with  benzine  to  make  a  paint  to  be 
applied  without  heating  is  said  to  give  good  results,  but  care  should 
be  used  to  get  a  coating  of  good  body  over  the  treated  wood.  Asphal- 
tum has  the  advantage  over  ordinary  lead  and  oil  paints  that  it 
becomes  plastic  when  warm  and  does  not  lose  this  property  soon. 
Oil  paints  harden  within  a  few  days  and  are  then  liable  to  crack. 


SUMMAEY 

Wood  decay  causes  very  serious  losses  in  deciduous  orchards  in 
California. 

It  begins  insiduously  below  dead  areas  and  spreads  extensively 
through  the  center  of  the  tree,  sometimes  killing  the  branches  but 
more  frequently  weakening  them  so  that  they  break  in  times  of  un- 
usual strain. 

Decay  of  wood  is  not  a  natural  result  of  old  age  or  weakness  but 
is  due  to  the  action  of  wood-destroying  fungi. 

The  process  of  the  destruction  of  wood  by  fungi  is  one  of  digestion 
and  absorption.  Where  complete  it  leaves  little  besides  ash,  the 
chemical  materials  of  the  wood  being  split  up  and  passing  off  as 
gases. 

Infection  evidently  takes  place  through  exposed  wood  and  more 
specifically  in  large  deep  cracks.  The  oak  root  fungus  forms  an  ex- 
ception in  that  it  is  able  to  kill  living  bark  and  penetrate  into  the  wood. 

Fruit  trees  vary  in  their  susceptibility  to  decay.  The  more  resist- 
ant will  doubtless  grow  for  many  years  as  hollow  trees. 

Statistics  which  have  been  gathered  show  that  about  fifty  per  cent 
of  all  bearing  trees  are  infected  with  wood  rot.  The  principal  fruit 
regions  all  suffer,  but  apparently  those  with  hot  and  trying  summers 
somewhat  more  than  the  cool  coast. 

Treatments  for  decaying  trees  must  follow  tree  surgery  methods 
and  are  probably  too  expensive  for  general  orchard  application. 

Prevention  offers  the  most  promise.  Proper  shaping  of  young 
trees  to  prevent  breaking  and  the  need  of  removing  large  limbs  is  the 
most  important  measure.  Where  large  limbs  must  be  removed,  and 
wherever  wood  is  exposed,  a  program  for  treatment  is  recommended, 
the  features  of  which  are : 

1.  Close  cutting  to  accelerate  healing. 

2.  Disinfecting  with  1-1000  corrosive  sublimate  solution  to  prevent 
the  growth  of  spores. 

3.  Sealing  with  hot  asphaltum  to  prevent  the  introduction  of  spores 
into  cracks  in  the  wood. 

4.  Inspection  of  all  trees  at  the  end  of  summer,  and  the  renewal 
of  the  disinfection  and  covering  of  all  exposed  wood  to  protect  it 
from  infection  during;  the  winter. 


For  additional  study  of  the  subject  of  this  circular  the  following 
references  are  suggested : 


Ltoto' 


Practical  Tree  Surgery,  J.  Franklin  Collins.  Reprint  from  the  Yearbook 
of  the  United  States  Department  of  Agriculture  for  1913.  May  be  purchased 
from  Superintendent  of  Documents,  Washington,  D.  C.     Price  10  cents. 

Practical  Tree  Repair,  etc.,  Elbert  Peets.  Published  by  McBride  Nast  and 
Company,  New  York,  1913.  Price  $2.00.  Very  highly  recommended  by  some 
of  our  best  tree  pathologists.  The  necessity  for  renewing  applications  is 
emphasized. 

Dressings  for  Pruning  Wounds  of  Trees,  A.  D.  Selby.  Circular  No.  126 
Ohio  Agricultural  Experiment  Station. 

Tree  Fillings  and  Wound  Dressings  for  Orchard  and  Shade  Trees,  A.  D. 
Selby.  Circular  No.  150  Ohio  Agricultural  Experiment  Station,  Wooster, 
Ohio. 

Citrus  Fruits,  etc.,  pp.  226-229,  J.  Eliot  Coit.  Published  by  MacMillan 
Company,  New  York,  1915.     Price  $2.00  net. 

Effect  of  Various  Dressings  on  Pruning  Wounds  of  Fruit  Trees,  G.  H. 
Howe.  Bulletin  No.  396  New  York  Agricultural  Experiment  Station,  Geneva, 
New  York.     Points  out  that  certain  dressings  on  wounds  may  delay  healing. 


DESCRIPTION   OF   PLATES 

Plate  I 
Fig.  1. — Peach  tree  top  worked  to  plum  about  five  years  before.     The  stub 
at  the  left  has  not  healed   over.     It  has  become  infected  and  sporophores  of 
the  oyster  shell  fungus  (Coriolus  versicolor  [Polystictus  versicolor])  are  forming- 
abundantly.     Limb  badly  sunburned  and  rotted. 

Fig.  2. — Sporophores  of  the  same  fungus  showing  the  lower  surface,  which 
is  composed  of  minute  tubes  or  pores  arranged  vertically.  Spores  are  formed 
in  these  tubes  and  fall  out  as  very  fine  dust. 

Fig.  3. — Part  of  the  same  group  of  sporophores  seen  in  Fig.  2,  showing  the 
upper  surface  which  is  felty-hairy  with  smooth  bands. 

Photographs  by  Mr.   W.   W.   Thomas. 


[10] 


PLATE  1 


Plate  II 

Fig.  1. — Pruning  cut  well  made  about  one  year  before,  on  French  prune. 
Note  the  deep  cracks  where  spores  might  easily  lodge  and  be  protected 
from  drying  long  enough  to  germinate.  Note  also  the  callus  just  beginning 
to  push  out  under  the  bark.  It  will  take  years  to  heal  over  this  cut  and, 
without  treatment,  the  cracks  are  open  to  infection  until  covered  over. 

Fig.  2. — Cut  well  made  at  the  top,  but  sloped  out  a  little  at  the  bottom. 
A  heel  has  died  and  the  callus  has  not  yet  covered  this,  while  the  top  is  nearly 
covered.     Note  the  cracks  in  the  exposed  wood. 

Fig.  3. — Cut  well  made,  callus  progressing  nicely  from  all  sides.  Note  the 
cracks.  Infection  may  have  occurred  or  may  yet  occur  before  the  wound  is 
covered.  At  a  is  a  small  cut.  Note  that  it  has  no  deep  cracks.  Orchardists 
agree  that  rot  rarely  starts  from  so  small  a  wound. 

Fig.  4. — Wound  healed  over.  If  infection  has  not  already  occurred,  wood 
rot  will  not  start  at  this  place.  Close  cutting  favors  prompt  healing  over 
and   thereby  lessens  the   danger   of  infection. 

Photographs  by  courtesy  of  Mr.  Earl  L.  Morris,  Horticultural  Commissioner 
of  Santa  Clara   County. 


12] 


K 


Ji 


PLATE  2 


STATION  PUBLICATIONS  AVAILABLE  FOR  DISTRIBUTION 


1897. 

1902. 
1903. 
1904. 
1914. 


No. 
168. 


REPORTS 

Resistant  Vines,  their  Selection,   Adaptation,   and  Grafting.      Appendix  to  Viticultural 

Report  for   1896. 
Report  of  the  Agricultural   Experiment   Station   for   1898—1901. 
Report  of  the  Agricultural  Experiment   Station   for    1901-03. 
Twenty-second  Report  of  the  Agricultural  Experiment   Station  for   1903-04. 
Report  of  the   College  of  Agriculture  and  the   Agricultural  Experiment   Statoin,   July, 

1913-June,  1914. 

BULLETINS 


Observations  on  Some  Vine  Diseases 
in  Sonoma  County. 

169.  Tolerance  of  the  Sugar  Beet  for  Alkali. 

170.  Studies  in  Grasshopper  Control. 
174.   A  New  Wine-Cooling  Machine. 

177.  A    New    Method    of    Making   Dry    Red 

Wine. 

178.  Mosquito  Control. 

184.  Report  of  the  Plant  Pathologist  to 
July  1,    1909. 

Report  of  Progress  in  Cereal  Investi- 
gations. 

The  California  Grape  Root-worm 

Grape  Culture  in  California ;  Improved 
Methods  of  Wine-making;  Yeast 
from   California   Grapes. 

The  Grape  Leaf-Hopper. 

Report  of  the  Plant  Pathologist  to 
July   1,    1906. 

The  Control  of  the  Argentine  Ant. 

The  Late  Blight  of  Celery. 

How  to  Increase  the  Yield  of  Wheat 
in   California. 

California   White   Wheats. 

The  Principles  of  Wine-making. 


185. 


195 
197 


198. 
203. 

207. 
208. 
211. 

212. 
213. 


No. 

216. 


220. 
225. 
227. 
230. 
234. 
241. 
242. 
244. 
246. 
248. 

249. 
250. 
251. 


252. 
253. 

254. 
255. 
256. 


A    Progress     Report    upon     Soil    and 

Climatic     Factors      Influencing     the 

Composition  of  Wheat. 
Dosage  Tables. 

Tolerance  of  Eucalyptus  for  Alkali. 
Grape  Vinegar. 
Enological    Investigations. 
Red  Spiders  and  Mites  of  Citrus  Trees. 
Vine  Pruning  in  California.     Part  I. 
Humus  in  California  Soils. 
Utilization  of  Waste  Oranges. 
Vine  Pruning  in  California.     Part  II. 
The  Economic  Value  of  Pacific  Coast 

Kelps. 
Stock  Poisoning  Plants  of  California. 
The  Loquat. 
Utilization    of    the    Nitrogen    and    Or 

ganic   Matter   in    Septic    and    Imhoff 

Tank  Sludges. 
Deterioration  of  Lumber. 
Irrigation   and   Soil   Conditions  in   the 

Sierra  Nevada  Foothills,  California. 
The  Avocado  in  California. 
The    Citricola    Scale. 
Value  of  Barley  for  Cows  fed  Alfalfa. 


CIRCULARS 

No.  No. 

65.   The  California   Insecticide  Law.  113. 

69.  The   Extermination   of   Morning-Glory.  114. 

70.  Observations    on    the    Status    of    Corn  115. 

Growing  in  California.  117. 
76.   Hot  Room  Callusing. 

79.  List  of  Insecticide  Dealers.  118. 

80.  Boys'  and  Girls'  Clubs.  119. 

82.  The     Common     Ground     Squirrels     of  121. 

California. 

83.  Potato  Growing  Clubs.  122. 
87.  Alfalfa. 

91.  Disinfection  on  the  Farm.  123. 

92.  Infectious    Abortion    and    Sterility    in 

Cows.  124. 

100.  Pruning  Frosted  Citrus  Trees.  125. 

101.  Codling    Moth    Control    in    the    Sacra-  126. 

mento  Valley.  127. 

106.  Directions  for  using  Anti-Hog-Cholera  128. 

Serum.  129. 

107.  Spraying  Walnut  Trees  for  Blight  and  130. 

Aphis  Control.  131. 

108.  Grape  Juice.  I32- 

109.  Community  or  Local   Extension  Work 

by  the  High  School  Agricultural  De-  133. 

partment.  I34- 

110.  Green  Manuring  in  California.  135. 

111.  The  Use  of  Lime  and  Gypsum  on  Cali-  136. 

fornia  Soils. 


Correspondence  Courses  in  Agriculture. 
Increasing  the  Duty  of  Water. 
Grafting  Vinifera  Vineyards. 
The    Selection    and    Cost    of    a    Small 

Pumping   Plant. 
The  County  Farm  Bureau 
Winery  Directions. 
Some    Things    the    Prospective    Settler 

Should  Know. 
The  Management  of   Strawberry   Soils 

in  Pajaro  Valley. 
Fundamental    Principles    of    Co-opera 

tion  in  Agriculture. 
Alfalfa  Silage  for  Fattening  Steers. 
Aphids  on  Grain  and  Cantaloupes. 
Spraying  for  the  Grape  Leaf  Hopper. 
House  Fumigation. 
Insecticide  Formulas. 
The  Control  of  Citrus  Insects. 
Cabbage   Growing   in    California. 
Spraying  for  Control  of  Walnut  Aphis. 
When      to      Vaccinate      against      Hog 

Cholera. 
County  Farm  Advisor. 
Control  of  Raisin  Insects. 
Official  Tests  of  Dairy  Cows. 
Melilotus    Indica. 


